To evaluate the use of multiple-labelled fluorescent microspheres for the measurement of regional myocardial blood flows in large hearts with fine resolution. The evaluation should provide: (1) assessments of accuracy relative to the standard microsphere approach, (2) an evaluation of the costs in terms of personnel time and programming development time for handling the data and the analysis for both standard applications and the more demanding applications intended for examining the fractal nature of the flow distributions in the normal heart. Since the data obtained with the proposed fluorescent microsphere techniques will provide accurate 3-dimensional information on deposition densities, the project allows, simultaneously with the evaluation, the gathering of new information relevant to the understanding of the relationship between the anatomy of the coronary branching network and the distribution of flows in a succession of physiological states, from vasopressin-induced vasoconstriction to states of dilatation induced by exercise and metabolic stimulus. The NIH, NHLBI, research grant, HL50238, entitled "Cardiac Metabolism and Flows," supports the basic animal studies that are alluded to in this proposal; the HL50238 grant is funded from September 30, 1992 through August 31, 1997. There is no duplication of effort in these complementary efforts. Specific Aims: 1. To evaluate the use of a technique for recording the positions of individual microspheres in three dimensions within the myocardium of the cardiac ventricles of the hearts of dogs. 2. To determine the efficacy and accuracy of obtaining regional flow estimates from analysis of the 3-dimensional data, given the dual problems of minor errors in estimation of sphere position and relatively larger errors in identifying and annotating the regional volumes within the heart, bounded as it is with irregular endocardial and epicardial surfaces. 3. To determine the feasibility for obtaining information on the 3-dimensional arrangement of the arterial bed in the heart using an already developed casting technique that fills only the arterial system down to the terminal arterioles.